1. Field of the Invention
The present invention relates to an electrostatic discharge protection structure and device. In particular, the invention relates to an electrostatic discharge protection structure and device that provide electrostatic protection for a liquid crystal display.
2. Descriptions of the Related Art
An electrostatic discharge phenomenon occurs when electrostatic energy is released into electrical circuits, and thus, suddenly causing a high transient voltage and current. The high transient voltage and current may damage the electrical circuits including the internal circuits and the internal conducting wires. Consequently, the protection of the internal circuits and pixel arrays from electrostatic discharge has become a serious concern.
When the electrostatic discharge phenomenon occurs, a large amount of heat is generated in a short period of time due to its high voltage and high current. In a liquid crystal display, due to the low coefficient of heat conductivity in the glass substrate, the heat generated by the electrostatic discharge phenomenon can not be conducted efficiently via the substrate within a short period of time. Consequently, if the electrostatic discharge current releases energy through high resistance paths rather than low resistance paths within a short period of time, the over-generated heat, without efficient dissipation, will damage devices on the display due to the large voltage drop in high resistance paths.
To solve problems caused by the electrostatic discharge phenomenon in liquid crystal displays, an electrostatic discharge protection device is conventionally disposed between the conductive wires of the pixel arrays of the liquid crystal display. The liquid crystal display is constructed by many pixel devices arranged in an array, wherein each of the pixel devices comprises a transistor to control the deflection degree of the liquid crystal. The deflection degree allows the liquid crystal to display various levels of brightness while the light generated from a backlight source is transmitted through the pixel device. Currently, a thin-film transistor is frequently used as a control transistor, which can be directly formed onto the glass substrate of the liquid crystal display. Consequently, the thin-film pixel array is formed with the pixel device array. The thin-film pixel array is controlled by a gate bus and a data bus. The gate bus comprises a plurality of conducting wires and each conducting wire connects with a plurality of thin-film transistor gates. Similarly, the data bus connects with a plurality of source/drains of the thin-film transistors. Each of the electrostatic discharge protection devices is disposed on each of the conducting wires as shown in FIG. 1. FIG. 1 shows a schematic view illustrating a conventional electrostatic discharge protection structure, wherein a data bus 11 connects to the source/drains of the thin-film transistors to write data therein, and a gate bus 12 connects to the gates of the thin-film transistors to turn-on or turn-off the thin-film transistors. FIG. 1 only shows the portion of the thin-film transistors in the thin-film pixel array. In this structure, each conducting wire of the data bus 11 and the gate bus 12 connects to an electrostatic discharge protection bus 13 through an electrostatic discharge protection device 101. It is noted that both ends of each conducting wire connects to the electrostatic discharge protection bus through the electrostatic discharge protection device 101.
Unfortunately, the conventional electrostatic discharge protection structure still has its drawbacks. With technological advances, drive circuits have been integrated with thin-film transistors. In other words, the drive circuit and the thin-film transistors are formed on the same substrate. With this integration, the conventional structure can not provide electrostatic discharge protection for the drive circuit, resulting in damage to the drive circuit on the display.
Furthermore, when the turn-on voltage of the designed electrostatic discharge protection devices is not high enough, the working voltage applied to the thin-film transistors during the panel of the display being lighted up will cause the current of the electrostatic discharge protection devices which connect with the thin-film transistors to leak. Because conventional electrostatic discharge protection structures dispose a large amount of electrostatic discharge protection devices around the thin-film pixel array, the current leakage will affect the normal operation of the display. When the conduction voltage of the electrostatic discharge protection device is excessively high, damage will occur to the devices on the display during electrostatic discharge due to the discharge current flowing through high resistance paths without an effective release of energy.
According to the aforementioned descriptions, an electrostatic discharge protection structure that not only is capable of protecting a liquid crystal display with an integrated drive circuit and thin-film transistor, but also can maintain normal operation during the current leakage of the electrostatic discharge protection device, is needed. Consequently, an integrated electrostatic discharge protection structure with electrostatic discharge protection devices and low current leakages needs to be developed in this field.